1. Field of the Invention
The present invention relates to a constant-meshing-type multi-speed transmission.
2. Description of Related Art
In a constant-meshing-type multi-speed transmission where drive gears on a main gear shaft and driven gears on a counter gear shaft are in a constant meshing state for every gear speed, in general, the gear shift is performed in such a manner that, when a shift pedal is operated, a dog clutch is moved in the axial direction so that the meshing of gears which effectively transmit power from a main gear shaft to a counter gear shaft is selected (see JP-A-2008-151275, for example).
In the case of the constant-meshing-type multi-speed transmission of a general type described in JP-A-2008-151275, due to the rotation of a shift spindle driven in response to a shift operation of a shift pedal, a shift drum is rotated by way of an intermittent drive mechanism, a shift fork is axially moved by being guided by a shift guide groove formed on an outer peripheral surface of the shift drum, and the shift fork moves a shifter gear and a shifter provided with a dog clutch mechanism on the main gear shaft and the counter gear shaft in the axial direction thus performing the gear shift.
Accordingly, the relatively large shift fork moving mechanism is interposed between the shift spindle and the counter gear shaft (and the main gear shaft) positioned on a lower side of the transmission and hence, the shift spindle and the counter gear shaft (and the main gear shaft) are largely spaced apart from each other. A transmission case rotatably supports the shift spindle and the counter gear shaft (and the main gear shaft) which are spaced apart from each other in such a manner.
On the other hand, with respect to the constant-meshing-type multi-speed transmission, there has been known a special multi-speed transmission where either the main gear shaft or the counter gear shaft rotatably supports gears in a relatively rotatable manner, and a control rod which moves axially in the inside of the gear shaft selectively operates engaging members arranged in the inside of the gear shaft so as to make a desired gear engage with the gear shaft thus establishing a gear speed. The applicant of this application previously filed the patent application on this special constant-meshing-type multi-speed transmission (see JP-A-2010-78050).
In the case of the special constant-meshing-type multi-speed transmission described in JP-A-2010-78050, a shift drum is provided adjacent to an end portion of the counter gear shaft in which the control rod passes through, and a small shift pin, which engages with the end portion of the control rod, is guided by a shift guide groove formed on the shift drum, and a gear shift is performed by the axial movement of the control rod.
Due to such a constitution, a relatively large shift fork moving mechanism such as one disclosed in JP-A-2008-151275 is unnecessary and hence, the miniaturization and reduction in weight of the multi-speed transmission can be realized.